For electrical apparatus used for sound processing and/or for producing sounds, such as synthesizers, mixers, and electrical instruments, it is very important to be able to produce or reproduce a sound such that it is perceived as close as possible to the real sound by a listener. In the field of music, musical dynamics of a sound or a tone, originating from for example an instrument or a voice, generally refers to the perceived volume of that sound or note, i.e. to the perceived loudness or softness of that sound, which is related to the level of force having been used for creating the sound or tone, as will be described below.
A sound includes a fundamental frequency, i.e. a pitch frequency fp, which is the perceived frequency of the sound. The sound may also include one or more component frequencies of the sound. The fundamental frequency fp and other component frequencies are known as partial frequencies (often denoted partials) of the sound. For some sounds, so called harmonic sounds, the one or more partial frequencies are integer multiples of the fundamental frequency fp. Such additional component frequencies of harmonic sounds are known as harmonics. For example, a harmonic sound S having a pitch of fp=440 Hz is a sound including a number of component frequencies fn=n*fp, where n is a positive integer. Thus the sound S includes a number of component frequencies such as 440 Hz, 880 Hz, 1320 Hz, and so on. The relative strengths of the component frequencies determine the timbre/tone of the sound S. In this example, the 440 Hz frequency component is known as the fundamental frequency.
Instruments such as e.g. a trumpet, a flute, and a violin generally produce harmonic tones. These instruments do however sound quite differently despite the fact that they have the same mutual frequency relationships for their pitch frequencies and component frequencies. The reason for these instruments sounding differently is, to a large extent, that they have different strengths of their respective component frequencies.
For some instruments/sounds, such as drum sounds, the component frequencies will typically not be integers of the fundamental frequency.
Musical dynamics is in this document defined as a measure of a level of force being perceived as having been used for producing a musical sound S or a tone. For example, for a piano tone, the musical dynamics is related to a level of force a key on the keyboard is perceived to have been pressed, where the musical dynamics is based on the character of the musical sound S or tone due to this force. Correspondingly, for a guitar, the musical dynamics is related to the level of force the guitarist is believed to have used to pluck the string on the guitar, where the musical dynamics is based on the character of the musical sound S or tone due to this force.
Correspondingly, for a drum, the musical dynamics is related to the level of force the drummer is perceived to have used to beat the membrane or body of the drum, where the musical dynamics is based on the character of the musical sound S or tone due to this force.
Also for e.g. a door closing, the musical dynamics is related to the level of force the person closing the door is perceived to have used to shut the door, where the musical dynamics is based on the character of the musical sound S or tone due to this force. A higher level of force here relates to a door being experienced to having been shut quickly and/or hard and a lower level of force relates to a door being perceived as having been shut slowly and/or softly.
As stated above, musical dynamics denotes as a measure of a level of force being perceived as having been used for producing a musical sound S or a tone, i.e. the musical dynamics is related to the perception of the timbre having been created. musical dynamics is not to be confused with the technical term signal dynamic, which is used e.g. in the fields of signal processing and acoustics. The term signal dynamic is mainly related to the amplitude and/or variation of the amplitude of the signal, and is not related to the perception of the timbre having been created. Also, musical loudness is not to be confused with the technical term loudness, which is sometimes used e.g. in home amplifiers for describing a change in frequency spectrum of a musical signal based on psycho-acoustics, which is a different type of loudness change that produces alterations of the sound that are unsuitable for the technical field of the present invention.
An alteration or change in musical dynamics for a sound means that a perceived loudness for that sound is increased or decreased, where the perceived loudness is related to a force used for creating that sound. In written musical notes, a composer can indicate the intended loudness, such as f (forte, strong/loud) or p (piano, soft), and thereby give the musician instructions on how the written notes are to be played regarding loudness.
A dynamic range includes a number of different possible levels of loudness this instrument or voice can produce, i.e. to the ability to vary the loudness of the sound being created.
Variations, such as alterations and changes, of the musical dynamics of a sound from a real instrument or a real voice change both the amplitude and the timbre of the sound. For example, an instrument being played loudly sounds brighter than when the instrument is played softly. Generally, when played softly, the instrument produces a more round tone, and when played loudly, the instrument produces a more shrill or bright tone. These differences in timbre between loudly and softly played instruments, respectively, are due to the fact that the relative amplitudes of the partials or the sound produced differ for loudly and softly played instruments.
For a softly played instrument, the frequency spectrum is usually dominated by frequency components near the pitch frequency fp, i.e. the fundamental frequency, since the amplitudes of the high partials are much lower than the amplitude for partials near the fundamental frequency. However, for a loudly played instrument, the number of high partials is higher than for the softly played instrument, and the amplitudes of the high partials are higher than for a softly played instrument. The amplitudes of the high partials can even be essentially as high as, or higher than, the amplitude for the fundamental frequency fp. For a listener, the sounds are perceived as being soft and as being loud, respectively.
Traditionally, to achieve different musical dynamics of a sound in electronic apparatus for sound processing, such as synthesizers, mixers and the like, the volume for a tone has simply been changed, or separate samples have been collected or produced for each level of loudness. To only change the volume results in a softer or louder sound, but also in poor sound quality, since the desired timbre variation can not be achieved. When utilizing separate samples for separate levels of loudness, e.g. for sampling a piano, samples were collected for each one of a number of loudness levels for each piano key. Basically, each piano key was pressed a number of times with differing force. It can be easily realized that the number of samples being required to achieve a tolerable dynamic range for an instrument is very large. This method therefore requires a very large number of sample collections and also a very large memory for storing these samples. It is also very difficult to sample and organize all this sound information without resulting in e.g. different piano keys and/or different touches of one piano key producing sounds being perceived as being uneven.
Another known method for altering the musical dynamics of a sound is to filter a signal containing the sound with a low pass filter (LP-filter). The LP filtering reduces the number of high partials and/or the amplitude of the high partials, which by a listener is perceived as the sound being made softer. However, the LP-filtering method results in an unrealistic timbre being produced, which is very annoying for a listener.
Shelf-filtering has also been proposed for altering the sound musical dynamics. However, the shelf-filtering solution has a problem in that it is difficult to control the filtering characteristics, such as the slope of the filter. Also, the shelf-filtering method is limited by the steepness of the slope of the filter characteristic. For example, for a biquad shelf filter, the slope is so flat that a number of filters may have to be used after each other in order to provide a steep enough slope for producing a desired timbre change. This leads to implementation complexity and/or an unrealistic timbre being produced.
Use of a large number of EQ-filters has also been proposed for altering the musical dynamics of a sound. Here, one filter was located at each one of the component frequencies being present. Thus, by the use of one filter at each component frequency, the amplitudes of the partials are directly reduced by applying a negative gain on them, thereby making the sound being perceived as softer. However, this method requires a large number of filters, which considerably adds to the system complexity. Also, if the sampling frequency is increased, or a sound having lower pitch is used, even more high partials appear in the sound, and each one of these additional partials has to be provided with a filter. Thus, a large and varying number of filters causing variable additional complexity results from this method.
As has been described above, the previously known solutions for altering musical dynamics of a sound thus provide inferior sound quality and/or systems having high complexity.